Remove unused functions applyEditingStyleToBodyElement() and applyEditingStyleToElement() in Editor

This patch removes following unused functions:
 - Editor::applyEditingStyleToBodyElement()
 - applyEditingStyleToElement()

BUG=n/a
TEST=n/a; no behavior changes
R=tkent@chromium.org

Review URL: https://codereview.chromium.org/23718006

git-svn-id: svn://svn.chromium.org/blink/trunk@157279 bbb929c8-8fbe-4397-9dbb-9b2b20218538